It has been reported that repeated phencyclidine (PCP) treatment induces schizophrenia-like behavior in mice. L-Tryptophan (Trp) concentrations in brain tissues of control (n = 8) and PCP-treated mice (10 mg/kg/day, s.c., 14 days, n = 10) were determined using high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC method involved pre-column fluorescence derivatization with (R)-(-)-4-(N,N-dimethylaminosulfonyl)-7-(3-isothiocyanatopyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-PyNCS). Eight different parts of the brain, namely, the frontal cortex, nucleus accumbens, striatum, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum, of both groups were investigated. A significant decrease in the L-Trp concentration in the nucleus accumbens (p = 0.024) and hippocampus (p = 0.027) was observed in PCP-treated mice, suggesting that alteration of the L-Trp metabolism might occur in these brain parts.